1. Field of the Invention
The present invention relates to a suck-back valve having a suck-back function that prevents the occurrence of leakage during the fully closing operation of an open/close valve.
This application is based on Japanese Patent Application No. 2008-209762, the content of which is incorporated herein by reference.
2. Description of Related Art
Conventionally, for example, for an open/close valve disposed in a pipeline system for liquid such as drug solution, a separate valve exclusively for “suck-back” has been additionally provided to prevent leakage (dripping of the fluid) that occurs during the fully closing operation. Such a valve exclusively for suck-back operates synchronously with closing operations of the open/close valve, and it is possible to prevent leakage by actuating a diaphragm in a direction that increases the volume of a suck-back chamber, thus sucking liquid on the outlet side to the suck-back chamber side (for example refer to Japanese Unexamined Patent Application, Publication No. 2002-316085).
However, in the above-described conventional valve exclusively for suck-back, because the open/close valve and the valve exclusively for suck-back are separate entities, there is a problem in that the apparatus as a whole requires a larger space for installation.
In addition, the open/close valve and the valve exclusively for suck-back are respectively operated by actuators that use air pressure, etc.; therefore, it is difficult to synchronize both actuators to reliably prevent leakage.
Furthermore, a suck-back valve using a diaphragm forms a large dead space in the suck-back chamber, thus posing the problem of low liquid replaceability. Moreover, in order to realize a large suck-back volume, the suck-back valve using a diaphragm requires an enormous suck-back chamber because the ratio of change of volume of the suck-back chamber when actuating the diaphragm is low, and thus, it is not practical.
Against such a background, there has been a need for a suck-back valve in which an open/close valve is provided with a suck-back function, i.e., a suck-back valve in which the open/close valve and the valve exclusively for suck-back are integrated, in order to reduce the installation space and to solve the problems of synchronization. In addition, in such a suck-back valve, a desirable suck-back structure is one that is capable of increasing the fluid replaceability by eliminating dead space in the suck-back chamber and capable of increasing the volume of fluid that can be sucked back.